This invention relates to the art of polybenzazole (PBZ) polymers and processes for synthesizing them.
Polybenzazole polymers are a known class of polymers comprising polybenzoxazole (PBO), polybenzothiazole (PBT), polybenzimidazole (PBI) and copolymers of these polymers that are described in Wolfe, Liquid Crystalline Polymer Compositions, Process and Products. U.S. Pat. No. 4,533,693 (Aug. 6, 1985); and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles 601 (J. Wiley & Sons 1988), which are incorporated herein by reference.
Polybenzazoles are generally classified as AB-polymers, containing a plurality of mer units depicted in formula 1(a), or AA/BB, containing a plurality of mer units which conform with formula 1(b) ##STR1## wherein:
each Ar is an aromatic group,
DM is a divalent organic moiety which is stable and inert under polymerization conditions, and
each Z is independently an oxygen atom, a sulfur atom, or a nitrogen atom that is bonded to a hydrogen atom or an organic moiety which is stable and inert in acid under polymerization conditions.
(For the purpose of this application, then the nitrogen atoms and Z moieties of a mer unit are depicted as bonded to an aromatic group without indicating their position, as in Formulae 1(a)-(b), it shall be understood that:
(1) each nitrogen atom and Z group within a given azole ring are bonded to the aromatic group in ortho position with respect to each other; and
(2) if the mer unit has two azole rings, one nitrogen atom and Z moiety may be in either cis position or trans position with respect to the other nitrogen atom and Z moiety, for example illustrated in 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, at 602 (J. Wiley & Sons 1988), which is incorporated herein by reference. The same understandings apply with respect to amine groups and Z moieties in a BB-PBZ monomer.)
Polybenzazoles are synthesized by (1) the reaction of at least one AA-PBZ monomer containing two electron-deficient carbon groups with at least one BB-PBZ monomer containing two o-amino-basic moieties and/or (2) the condensation of one or more AB-PBZ monomers containing an aromatic group, an o-amino-basic moiety and an electron-deficient carbon group The reaction is illustrated generally in Formula 2: ##STR2## wherein each Q is an electron-deficient carbon group and all other moieties have the meaning and preferred embodiments previously given.
The divalent organic moiety DM of the AA-monomer ordinarily comprises an aromatic group, which is most usually a p-phenylene group. The reaction is ordinarily carried out under non-oxidizing conditions in a non-oxidizing, dehydrating solvent acid, which is most frequently polyphosphoric acid.
The known reaction conditions are unsuitable for synthesizing large quantities polybenzazole polymer. The most commonly used reaction techniques, as described in U.S. Pat. No. 4,533,693, which is previously incorporated by reference, require days to synthesize a few hundred grams of high molecular weight polymer. What is needed is a process to quickly polymerize polybenzazole polymers of high molecular weight.